1. Technical Field
The present invention relates to storage-disk drive motors for spinning for example hard disks and like storage disks, wherein the motors have dynamic-pressure bearings for supporting the storage disk rotation. In particular the present invention relates to storage-disk drive motors having dynamic-pressure bearings for supporting rotation of storage disks of small outside-diameter, such as 1-inch.
2. Description of Related Art
Miniature and thin storage-disk drive motors for driving hard disks and like storage disks are known. Such an example is the motor disclosed in Japanese Laid-Open Patent Application No. 09-46938. This conventional storage-disk drive motor is provided with a bracket, a rotor hub outer-circumferentially carrying a storage disk and supported by a pair of ball bearings so as to be rotatable relative to the bracket; a rotor magnet fixedly fitted to the rotor hub; and a stator disposed so as to radially oppose the rotor magnet.
Nevertheless, in motors thus employing ball bearings to support rotation of the rotor hub, bearing rigidity is largely due to the diameter of the balls used. In driving for example 1-inch outside-diameter storage disks, however, the diameter of the mounting hole formed in the center of the storage disk for mounting it on the rotor hub will only be approximately 6 mm. This not only restrains the dimension of the balls that may be used for the ball bearings to a diameter that leaves rotation of the rotor hub unstable, but also compels miniaturizing the shaft and making other structural parts thin-walled, such that it is difficult to maintain sufficient mechanical strength in the motor.
There are, furthermore, storage-disk drive motors wherein instead of the ball bearings as described above, dynamic-pressure bearings are used for supporting rotation of the rotor hub. Such an example is the motor disclosed in Japanese Laid-Open Patent Application No. 09-166145. This conventional motor has a pair of radial bearings as means that support radial loads; and further a pair of thrust bearings as means that support axial loads. The radial bearings retain a lubricant in a micro-gap defined between the shaft and the inner circumferential surface of a sleeve member that radially opposes the outer circumferential surface of the shaft. Dynamic pressure-generating grooves consisting of herringbone striations are formed on the outer circumferential surface of the shaft so as to generate dynamic pressure in the lubricant during rotation of the rotor hub.
Likewise, the thrust bearings retain a lubricant in a micro-gap defined between a disk-shaped thrust plate fastened to the end of the shaft, and the end face of the sleeve member and the upper face of the thrust cover, which axially oppose the top/bottom faces of the thrust plate. Dynamic pressure-generating grooves consisting of spiral striations formed on the top/bottom faces of the thrust plate generate dynamic pressure in the lubricant during rotation of the rotor hub.
Nevertheless, personal computers using storage-disk drive devices continue to be made smaller and thinner. What is more, storage-disk drive devices have come to be used in compact equipment such as digital cameras. This calls for miniaturizing and making thinner the storage-disk drive motor itself.
Employing dynamic-pressure bearings instead of ball bearings has done away with the effects of the ball diameter, and has made it possible stably to sustain rotation of the rotor hub. With there being a pair of radial bearings, however, it is very difficult to miniaturize the motor and make it thinner overall while maintaining satisfactory assembly precision, and joint strength in the shaft and thrust plate joint.